It is feasible from the Python Console window. 
Opacity is a layer property, so it is possible to set it with a simple attribution. 

Go to `filters->Python Fu->Console`  - there you can type Python expressions. The first one you want is to get a reference to your image - for example:
`img = gimp.image_list()[0] ` (press `enter`afterwards)  willgt you a reference to the latest (rightmost tab) open image in GIMP. (increase the numbers from 0 inside the brackets to get to the other images)

The layers are available as a Python list when you ype img.layers, and the opacity varies from 0.0 to 100.0  - so, the first thing to do is to calculate how much you want to increase the opacity from one layer to the next - that number is:
`opacity_step = 100.0 / len(img.layers)` 
(just type the variable names, like `img` and `opacity_step` by themselves and press enter to check their values).
Now, just pick a starting opacity - ex. `current_opacity = 0.0` and then iterate over all layers with a  `for` command, setting the opacity. So, putting everything together, you should type:


    img = gimp.image_list()[0]
    opacity_step = 100.0 / len(img.layers)
    current_opacity = 0.0
    for layer in reversed(img.layers):
        layer.opacity = current_opacity
        current_opacity += opacity_step